1. Field of the Invention
The present invention relates to a light shielding structure of an optical apparatus.
2. Description of the Related Art
In an optical apparatus such as a camera, various kinds of light shielding structures have been proposed in order to shield harmful reflected light within an optical path. For example, a light shielding structure in which matte black coating (antireflection coating) is applied, or flock paper is pasted on a reflecting portion has been proposed. Furthermore, Japanese Laid-Open Patent Application Publication No. H11-305098 has disclosed a structure in which a light-shielding member (flare cutter) protruding in the direction orthogonal to the optical axis is provided.
However, there is a case in which it is difficult to provide the above-described light shielding structure due to structural reasons, or difficult to produce a satisfactory light shielding effect. One example is shown in FIGS. 1 and 2, in which first and second relatively-movable members 11 and 12 are relatively moved in an optical axis direction (with respect to each other) to change an overlapped area therebetween. FIG. 1 shows an operational state of the optical apparatus, and FIG. 2 shows a non-operational state of the apparatus. In FIGS. 1 and 2, OA denotes an optical axis of an optical system, and CF denotes an image surface.
In the non-operational state shown in FIG. 2 of the optical apparatus, the first relatively-movable member 11 and the second relatively-movable member 12 overlap each other by almost the entire areas thereof. Whereas, in the operational state shown in FIG. 1 of the optical apparatus, the first relatively-movable member 11 and the second relatively-movable member 12 are relatively moved to cause a positional relationship such that the mutually overlapped area therebetween is reduced. For example, a lens barrel of a compact camera is a well known optical apparatus which is provided with relatively-movable members having mutually overlapping areas as described above according to whether the apparatus is in an operational state or a non-operational state. Moreover, in the operational state shown in FIG. 1, a part of the inner surface 11a on the optical axis side of the first relatively-movable member 11 is exposed to the optical path (the optical axis OA), and reflected light by the inner surface 11a on the optical axis side enters an image surface CF as shown by an arrowhead in FIG. 1, causing an adverse effect.
In order to control internal reflection by the first relatively-movable member 11, it is conceivable to, for example, apply antireflection coating onto the inner surface 11a on the optical axis side, or paste flock paper on the inner surface 11a on the optical axis side. However, when the distance between the first relatively-movable member 11 and the second relatively-movable member 12 is small, there is a possibility that interference occurs between the antireflection coating or the flock paper provided on the inner surface 11a on the optical axis side and the second relatively-movable member 12. When the distance between the first relatively-movable member 11 and the second relatively-movable member 12 is several scores of micrometers because, for example, the flock paper has a thickness of about 100 through 200 micrometers, even if the paper is thin, there is a possibility that a load is applied by repetitive relative movement between the first relatively-movable member 11 and the second relatively-movable member 12, so that the paper is peeled off or a resistance is caused due to this relative movement. Moreover, control of a film thickness of an antireflection coating is difficult, especially, in the case of a brush coating. Accordingly, such a coating is not appropriate for a light shielding structure for use when the distance between the first relatively-movable member 11 and the second relatively-movable member 12 is small. Furthermore, when light rays enter at a large incident angle in such a way that almost perfect reflection from the inner surface 11a on the optical axis side occurs, there is a possibility that a satisfactory light shielding effect may not obtained, even if the antireflection coating is applied.
Although another method for controlling the internal reflection is possible, wherein a ring-like light shielding member is provided at the rear end portion of the first relatively-movable member 11, this undesirably causes the whole structure to increase in size and become more complex. Moreover, in some cases, it is not appropriate to provide the light shielding member at the rear end position of the first relatively-movable member 11, because a normal light which correctly travels along the optical path and an internal reflection light overlap each other to cause a state in which it is difficult to shield only the internal reflection light. Furthermore, when the rear end portion of the first relatively-movable member 11 is a sliding portion, it is difficult to provide the light shielding member at this rear end portion.